Macronutrient Self-Selection Pattern in Rats under Different Lighting Conditions

The effect of constant darkness (DD) and constant light (LL) on the circadian pattern of macronutrient self-selection, daily food intake and body weight was analysed in rats using an automated computer system. No significant differences in energy intake were observed between groups as regards energy intake or macronutrient preferences. Fat and CHO intakes showed a negative correlation (p < 0.005 in LL and p < 0.0005 in DD and LD), while protein intake remained constant, which suggests the existence of separate regulation mechanisms governing the intake of protein and energy. Energetic requirements can be preponderantly covered by CHO or fat, depending on the preferences of the animal. Body weight measurements reflected no significant variations between groups at the end of the experiment. However, the circadian pattern of wheel-running activity and the intake of the three macronutrients measured in both constant lighting conditions varied with respect to that observed in LD. This was particularly true in the case of LL, when constant illumination exerted a decoupling effect on the rhythms. The results indicate that lighting conditions modulate the circadian pattern of wheel-running activity and macronutrient intake. However, changes in temporal organisation of food intake did not affect macronutrient preferences, daily energy intake, number of meals, feeding duration or body weight, suggesting the existence of a double, circadian and homeostatic, control of such variables.     

Predator-prey coevolution driven by size selective predation can cause anti-synchronized and cryptic population dynamics

Population dynamics and evolutionary dynamics can occur on similar time scales, and a coupling of these two processes can lead to novel population dynamics. Recent theoretical studies of coevolving predator-prey systems have concentrated more on the stability of such systems than on the characteristics of cycles when they are unstable. Here I explore the characteristics of the cycles that arise due to coevolution in a system in which prey can increase their ability to escape from predators by becoming either significantly larger or significantly smaller in trait value (i.e., a bidirectional trait axis). This is a reasonable model of body size evolution in some systems. The results show that antiphase population cycles and cryptic cycles (large population fluctuation in one species but almost no change in another species) can occur in the coevolutionary system but not systems where only a single species evolves. Previously, those dynamical patterns have only been theoretically shown to occur in single species evolutionary models and the coevolutionary model which do not involve a bi-directional axis of adaptation. These unusual dynamics may be observed in predator-prey interactions when the density dependence in the prey species is strong.     

Single generation cycles and delayed feedback cycles are not separate phenomena

We study a simple model for generation cycles, which are oscillations with a period of one or a few generation times of the species. The model is formulated in terms of a single delay-differential equation for the population density of an adult stage, with recruitment to the adult stage depending on the intensity of competition during the juvenile phase. This model is a simplified version of a group of models proposed by Gurney and Nisbet, who were the first to distinguish between single-generation cycles and delayed-feedback cycles. According to these authors, the two oscillation types are caused by different mechanisms and have periods in different intervals, which are one to two generation times for single-generation cycles and two to four generation times for delayed-feedback cycles. By abolishing the strict coupling between the maturation time and the time delay between competition and its effect on the population dynamics, we find that single-generation cycles and delayed-feedback cycles occur in the same model version, with a gradual transition between the two as the model parameters are varied over a sufficiently large range. Furthermore, cycle periods are not bounded to lie within single octaves. This implies that a clear distinction between different types of generation cycles is not possible. Cycles of all periods and even chaos can be generated by varying the parameters that determine the time during which individuals from different cohorts compete with each other. This suggests that life-cycle features in the juvenile stage and during the transition to the adult stage are important determinants of the dynamics of density limited populations.     

Geological cycles

Abstract

Deep body temperature (DBT) and heart rate (HR) circadian rhythms were determined by radiotelemetry in 4 mares kept under controlled light and temperature conditions. Ovulations were determined by rectal palpation of their ovaries. Mean DBT values ranged from 35.85 ± .04 to 37.22 ± .02°C The circadian range of oscillation was extremely low, approximately 0.5° C, with time of maximum temperature occurring midway through the dark period. Mean HR values ranged from 36.4 ± 1.7 to 53.0 ±3.6 beats per min. The circadian range of oscillation was also low, less than 15 beats per min with time of maximum HR occurring approximately at the time of lights off. The HR circacadian rhythm peaked before the DBT circadian rhythm by 3 to 8 hrs. Ovulation did not appear to consistently affect DBT and HR circadian rhythms or their phase relationships.     

Boom, bust, and the human body: Further evidence on the relationship between height and business cycles

Historical time series for average human height exhibit short- and medium-term cycles that can be associated with business cycles in the 19th and 20th century. Using spectral analysis, we calculate the proportion of cyclical fluctuations in height series attributable to economic cycles. We also analyze the extent to which these cyclical phenomena change over time. In the U.S., the association between height cycles and business cycles was weaker among richer segments of the society, and weaker among men than among women. Additionally, the relationship diminished over time, probably with the rich preceding the population at large.     

Semilunar spawning cycles ofFundulus similis (Cyprinodontidae)

Synopsis The longnose killifish,Fundulus similis (Cyprinodontidae), spawns with a semilunar periodicity during an extended breeding season (March through August) along the Alabama (U.S.A.) Gulf coast. Spawning characteristically occurs during the 3–6 days of the ascending and spring tides of each semilunar tidal cycle. Such spawning cycles appear to be a relatively common adaptation within the reproductive strategies of intertidal cyprinodontids.     

Change in Hair Cycle and Hair Length in Nude Mice by Administration of Deuterium Oxide

D₂O increased hair length in Balb/c nu/nu (nude) mice in our previous study although it has an antimitotic effect in cells. To investigate the mechanism of the effect on the hair length, we examined the change by the administration of D₂O in the duration of the hair cycle and the proliferating activity of the hair matrix in relation with hair length in nude mice. The results showed that 20 or 30% D₂O administration did not change the gross structure of the hairs, the proliferative activity and keratinization of the hair matrix cells, but elongated the hair cycle. The duration of the hair cycle increased by the administration of D₂O in a dose-dependent manner over the examined range and these effects were reversible by discontinuation of D₂O. The change in the hair length correlated with the change in the hair-existing phase particularly. We also showed that the mast cell density in the skin, which is related to the hair cycle, increased in the deuterated mice at anagen VI stage which nearly corresponds to the hair-existing phase. The increase in the mast cell density may be related to the increase in the hair cycle duration. These findings indicate that the increase in hair length may be due to the increase in the duration of the hair cycle, in particular, an increase in the hair-existing phase. This study thus suggests that D₂O slows not only short-term cycles such as circadian clock or ultradian clock, but also the hair cycle which is a long-term cycle.